1. Field of the Invention
The present invention relates to the molding of a part around an insert. More particularly, the present invention provides methods and apparatus which may be used, for example, in the injection molding of a part around an insert such as a bearing assembly.
2. Description of Related Art
In order to provide an insert in a molded part, the insert is generally either placed into the mold prior to the molding process, or is inserted into the part after molding has been completed. Positioning the insert in the mold prior to the molding operation can be problematic, particularly when a portion of the insert must remain exposed (i.e, not covered by the molding material, such as plastic). For example, during plastic injection molding, molten plastic is urged into a mold cavity. If an insert is positioned in the mold cavity prior to the injection of molten plastic, the heat and pressure required during the injection of molten plastic may deform or otherwise damage the insert. In addition, in order to ensure that a portion of the insert is not covered by the plastic, that portion of the insert must be masked or otherwise protected without interfering with the molding process. Proper alignment of the insert in the mold cavity can also be difficult.
As an alternative to molding the part around the insert, a two-step process may be employed wherein the part is first molded without the insert present. Thereafter, the insert is inserted into a suitably-sized recess or other opening in the molded part. This two-step method, however, is labor intensive. In addition, it can be difficult to properly align the insert within the part, and to ensure that the insert remains in place. For example, an insert such as a bearing assembly may need to be secured within a recess in the part by adhesive or other suitable means.
The present invention provides a pin for use in molding a part around an insert, wherein the pin comprises:
(a) a shaft; and
(b) a head portion positioned at one end of the shaft, the head portion having a sharp edge extending about at least a portion of its circumference.
The pin is configured such that it may be positioned in a mold above an insert so that the molding material will flow across the upper surface of the head portion of the pin into the mold.
In another embodiment of the present invention, a method of molding a part around an insert is provided. This method comprises the steps of:
(a) providing an insert (such as a bearing assembly), the insert having a passageway therethrough;
(b) providing a pin, the pin comprising a shaft and a head portion positioned at one end of the shaft, the head portion having a sharp edge extending about at least a portion of its circumference;
(c) positioning the pin and the insert within a mold for a part to be molded, with the shaft of the pin positioned within the passageway of the insert;
(d) flowing molding material (such as plastic, rubber or metal) across the upper surface of the head portion of the molding pin into the mold and about the insert, thereby forming a part having the insert therein; and
(e) urging the pin away from the part such that the sharp edge of the head portion releases the pin from the part.
In yet another molding method according the present invention, a method of molding a part around an insert comprises:
(a) providing an insert, the insert having a passageway therethrough;
(b) providing a pin, the pin comprising a shaft, a head portion positioned at one end of the shaft, and a bore which extends at least partially through the shaft;
(c) providing a mold, the mold including an alignment member;
(c) positioning the pin and the insert within a mold for a part to be molded, with the shaft of the pin positioned within the passageway of the insert, and the alignment member of the mold extending at least partially into the bore; and
(d) flowing molding material across the upper surface of the head portion of the molding pin into the mold and about the insert, thereby forming a part having the insert therein.